A color cathode ray tube of a shadow mask type has electron beams emitted from an electron gun which pass through apertures of the shadow mask to land on R, G, and B blue pixels, respectively, on a phosphorescent layer.
However, part of the electron beams pass through the apertures of the shadow mask and the rest strike the inner surface of the shadow mask so as to heat it. As a result, the shadow mask is thermally expanded and domes out, so that the position of the apertures is changed against the electron beams. Thus, a demand for compensating the change is proposed.
As a conventional method of solving the doming of the shadow mask, corner springs called hook springs are interposed between stud pins installed at a predetermined position on the inside of a face panel and a frame suspended from the stud pins so as to compensate the changing position of the apertures caused by the doming.
The corner springs are installed at the middle part or at the corners of the long and short sides of the frame.
A structure having corner springs installed on the corners of the frame has the advantage of suppressing the free vibrations of the frame.
The above method is disclosed in the U.S. Pat. Nos. 3,894,260, 3,935,496 and 3,986,071.
The suspending systems of the above inventions have in common clamping members attached to the edge of the frame.
The clamping member is provided with a pair of tension arms and the corner springs, so that it is welded at a predetermined position to the frame or connected to the frame by a locking member.
However, the above suspension system results in the increase of elements. Due to the complex structure, attaching and detaching the frame, performed many times during the assembling process, is difficult and more likely to change the elements.
Especially, the U.S. Pat. No. 3,894,260 proposes a new structure such that a stud member to support the end of the corner spring is installed on all edges of the face panel. However, it can not be manufactured with the manufacturing equipment of a conventional color cathode ray tube.
Since the face panel disclosed in the U.S. Pat. Nos. 3,921,024 and 3,935,496 should have a recess at all edges of the face panel having a corner spring, a metal mold for face panel, should be prepared.
The U.S. Pat. No. 3,986,071 discloses a structure in which a pair of stud pins are installed on the corner of the face panel to support both ends of the corner spring. However, this structure has the disadvantage of the unsettled suspending state of the corner spring.
The simplest corner spring structure supporting the corners of the frame is described in FIG. 4. This structure is proposed in the U.S. Pat. No. 4,652,792.
The corner spring 2 described in '792 has a welding plate 8 attached to the side wall of the solid frame 6 supporting the shadow mask and the one side end of a supporting plate 10 united together with the welding plate 8 by a weldment. The supporting plate 10 is outwardly bent in a V shape against the welding plate and the end of supporting plate 10 and is extended parallel to welding plate 8 to form a plate 16. The plate 16 has a hole 18 into which the stud pin 14 penetrates.
FIG. 5 shows an assembling state where the supporting plate 10 forms a predetermined angle .theta. against the plate 16.
Here, a relationship of a deflecting angle .beta. between an electron gun and an effective face of the shadow mask 4 and a bending angle .theta. of the supporting plate is .theta.+.beta.=90.degree..
However, this new suspension system also has some problems in the attaching and detaching process which is performed many times during an assembling process.
The supporting plate 10 receives a force applied in the direction of arrow x as shown in FIG. 4, so that, it is bent as a dotted line, as shown in FIG. 5, to be plastically deformed in a predetermined angle .theta..
In addition, since the weight of frame 6 is concentrated in the supporting plate 10, when frame 6 is vibrated in the direction of arrow Y as shown in FIG. 4, the supporting plate 10 is twisted against the welding plate 8.
Japanese Patent Laid-Open Nos. 89-117242 and 89-117243 propose a solution for the above deformation problem.
However, any conventional technique has such a structure that a displacement of the frame by the thermal expansion can not agree to the deflecting angle .beta. of the electron beam.
Thus, an initial operation of the conventional color cathode ray tube results in a misconvergence and mislanding which lengthens the picture display time.